jackboot (n.) Look up jackboot at Dictionary.com
also jack-boot, 1680s, type of large, strong over-the-knee cavalry boot of 17c.-18c., later a type worn by German military and para-military units in the Nazi period. From jack (n.), though the exact sense here is unclear + boot (n.1). Figurative of military oppression since 1768. Related: Jackbooted.